I am not sure what is going on to be honest, I have another card layout system in my code and it works fine.

Summary of what I noticed :
1. there are no errors.
2. when I try to switch from Panel A to Panel B, the whole thing freezed.
3. when I try to switch from B to A, the .show() line has been ran, but A didn't show up and B keep running.
4. println are put all over the place(I removed most of them now) and I am quite sure the .show() command is being excute but nothing happens.
I'll be monitoring this post closely if any of you want addition information.

Core.java (where the main is in, also the Frame and the card layout in question, this is the code that most likely to have something wrong with it)